Holding furnaces are reservoirs for holding and maintaining molten material in its molten state. There are generally two types of holding furnaces: castable lined holding furnaces and board lined holding furnaces. Within these groups, there are many types and grades of non-wetting castable refractory and non-wetting insulating refractory available. A board lined furnace, for example, may be lined with calcium silicate boards or blocks, but it may also be lined with many other different materials that are interchangeable with the calcium silicate. The calcium silicate board lined holding furnaces, however, are generally considered to be more energy efficient than the traditional castable lined holding furnaces.